CA1194926A - Ribbed substrate for fuel cell electrode - Google Patents
Ribbed substrate for fuel cell electrodeInfo
- Publication number
- CA1194926A CA1194926A CA000435102A CA435102A CA1194926A CA 1194926 A CA1194926 A CA 1194926A CA 000435102 A CA000435102 A CA 000435102A CA 435102 A CA435102 A CA 435102A CA 1194926 A CA1194926 A CA 1194926A
- Authority
- CA
- Canada
- Prior art keywords
- ribbed
- layer
- substrate
- fuel cell
- ribbed layer
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
- H01M4/00—Electrodes
- H01M4/86—Inert electrodes with catalytic activity, e.g. for fuel cells
- H01M4/96—Carbon-based electrodes
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/30—Hydrogen technology
- Y02E60/50—Fuel cells
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
- Y10T428/24479—Structurally defined web or sheet [e.g., overall dimension, etc.] including variation in thickness
- Y10T428/2457—Parallel ribs and/or grooves
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
- Y10T428/24479—Structurally defined web or sheet [e.g., overall dimension, etc.] including variation in thickness
- Y10T428/24595—Structurally defined web or sheet [e.g., overall dimension, etc.] including variation in thickness and varying density
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
- Y10T428/24479—Structurally defined web or sheet [e.g., overall dimension, etc.] including variation in thickness
- Y10T428/24612—Composite web or sheet
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
- Y10T428/24942—Structurally defined web or sheet [e.g., overall dimension, etc.] including components having same physical characteristic in differing degree
- Y10T428/24992—Density or compression of components
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/249921—Web or sheet containing structurally defined element or component
- Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
- Y10T428/00—Stock material or miscellaneous articles
- Y10T428/249921—Web or sheet containing structurally defined element or component
- Y10T428/249953—Composite having voids in a component [e.g., porous, cellular, etc.]
- Y10T428/249981—Plural void-containing components
Abstract
TITLE OF THE INVENTION:
RIBBED SUBSTRATE FOR FUEL CELL ELECTRODE
ABSTRACT OF THE DISCLOSURE:
A porous ribbed substrate for a fuel cell electrode is herein disclosed which has a ribbed layer on one side and a non-ribbed layer on the other side, the non-ribbed layer having a bulk density smaller than the bulk density of the ribbed layer.
The fuel cell electrode substrate has a porosity of 50 - 80% and good mechanical strength such as a bending strength of not less than 50 kg/cm2. A fuel cell prepared from the electrode substrate has excellent properties.
RIBBED SUBSTRATE FOR FUEL CELL ELECTRODE
ABSTRACT OF THE DISCLOSURE:
A porous ribbed substrate for a fuel cell electrode is herein disclosed which has a ribbed layer on one side and a non-ribbed layer on the other side, the non-ribbed layer having a bulk density smaller than the bulk density of the ribbed layer.
The fuel cell electrode substrate has a porosity of 50 - 80% and good mechanical strength such as a bending strength of not less than 50 kg/cm2. A fuel cell prepared from the electrode substrate has excellent properties.
Description
The present ln~ention relates to a fuel cell electrode substra-te, particularly an electrode substrate having a double laye~
structure, that is herein termed by "a ribbed layer" and "a non-rib~ed layer", each layer having di~ferent properties from one another.
A ribbed electrode substrate for a monopolar Euel cell has been developed which has a ribbed surface on one side and on the other side a flat surface with a catalyst layer on the surface thereof. Such an electrode substrate is carbonaceous and porous as a whole. A cell is composed of two electrode substrates with a catalyst layer and a matrix therebetween for holding electrolyte. In a stack of such cells to form a fuel cell, a separator plate is disposed between two adjacent cells in contact with ribs of the substrate. Reactant gases (hydrogen as a fuel gas and oxygen or air) are fed via channels formed between the ribs and the separator plate and the gases diffuse from the ribbed surface to the flat surface in the electrode substra-te to reach the catalys-t layer.
For preparing such an electrode substra-te, the following I methods previously proposed may be used. For example, one method for preparing a general electrode substrate was proposed in Japanese Patent Application Laying Open No. 166354/82 wherein a mixture based on short carbonaceous fibers is pressed to form a porous shaped article. Another proposed method was described in Japanese Patent Publication No~ 18603~78 in which method a machined paper of carbon fibers is impregnated with an organic polymer solution and is made into a porous carbon fiber paper.
, i, A still another method for preparing an electrode substrate was proposed in United States Patent ~o. 3,829,327 wherein a web of carbon fibers is subjected to chernical vapor deposition of carbon to form a porous electrode substrate.
These electrode substrates have substantially homogeneous monolayer structures.
Such a homogeneous monolayer electrode substrate has however, disadvantages such as follows: with a high bulk density of a substrate, there is obtained a low limiting current density due to less diffusion of reactant gases and a rapid deterioration of performance of a fuel cell due to insufficient storage of electrolyte in the sub-strate, and therefore the life of a fuel cell is shortened;
on the other hand, disadvantages are high electric and thermal resistance and a low mechanical strength such as a bending strenqth, with a low bulk density of an electrode substrate.
It is an object of the present invention to provide an electrode substrate without such disadvantages.
According to the present invention, there is pro-vided a ribbed porous substrate for a fuel cell electrode, having a bending stength of not less than 50 kg/cm2 and a porosity of 50-80~, not less than 70~ of pores being open pores and not less than 60~ of the pores having a diameter in the range of 5-50 ~m, which comprises a double layer structure consisting essentially of a ribbed layer having ribs on one side thereof and a non-ribbed layer having flat surface on both side thereof and having a bulk density lower than the bulk density of the ribbed layer, the non-ribbed layer being laminated onto a flat s~rface of said ribbed layer and the laminated sheet being calcinated.
The ribbed layer of the electrode substrate of the S present invention has ribs on the outer surface thereof to be abutted to a separator plate in a fuel cell. The ribs may form together with the separator U-shaped channels for feeding reactant gases. The ribbed layer of the substrate preferably has a bulk density of 0.5 - 0.8 g/cm3 in order to provide the electrode substrate with a desired mechan-ical strength such as a bending strength of not less than 50 kg/cm2. The thickness of the ribbed layer except ribs is from 1/4 to 5/6 of the total thickness of the electrode substrate minus a thickness of the ribs.
The non-ribbed layer of the electrode substrate according to the invention has a flat surface on the outer side thereof and a bulk density lower than the bulk density of the ribbed layer. The bulk density of the non-ribbed layer is preferably in the range of 0.4 - 0.6 g/cm3 for a desired diffusion or permeation of reactant gases and for a desired holding of a given amount of catalyst and electrolyte.
Generally, it is desirable for a fuel cell that a good diffusion of reactant gases through pores in the electrode substrate is maintained in the whole part of the substrate. In the present invention, the electrode sub-strate is porous as a whole and has a porosity of 50 - 80 and not less than 70~ of L?~ t ~i the pores are open pores. Furthermore, the diameter of pores in the substrate of the invention is distributed in a narrow range, that is to say, not less than 60% of the pores have diameter in the range of 5 - 50 ~m, this sharp distribution of pore diameter resulting in a better application of the e]ectrode substrate of the invention to a fuel cell.
The electrode substrate of the present invention may be prepared by various methods, for example pressing process, paper-machining process or coating process. In the pressing process, raw materials for each layer, i.e. a non-ribbed layer and a ribbed layer, are separately supplied in-to a die having a predetermined configuration and pressed while heating. In the paper-machining process, a machined paper of mixed carbon fibers as a non-ribbed layer is laminated onto a pressed part prepared from the same raw material as the pressing process for a ribbed layer. In the third method (the coating process), a mixture of a filler e.g. active carbon or carbon black and a thermosetting resin e.g. a liquid phenol resin (in an alcohol as a solvent~
as a non-ribbed layer is coated onto a pressed part prepared from the same raw material as the pressing process for a ribbed layer.
A raw material for the ribbed layer of the invention may be appropriately selected from carbon fiber and active carbon for a filler, a polymer substance with a sharp distribution of particle diameters such as polyvinyl alcohol, polyethylene, polypropylene, polyvinyl chloride and sugar for a pore regulator and thermosetting resins such as phenol resin for a binder.
A raw material for the non-ribbed layer of the invention may be suitably selected Erom known materials to be appropriately used depending on to the processes. In the pressing process, a filler may be carbon fiber, granular active carbon or the like, a pore regulator may be the same as for the ribbed layer and a binder may be phenol resin or the like. In the paper-machining process, a filler may be carbon fiber or the like, ~ a pore regulator may be polyvinyl alcohol fiber or the like and a binder may be liquid phenol resin or the like. In the coating process, a filler may be granular active carbon, carbon black or the like, a pore regulator may be the same as -the pressing process and a binder may be the same as the paper-machining process.
As an example of the preparation process of the electrode substrate of the present invention will be described hereinafter in more detail, particularly the pressing process using short carbon fiber as a filler, granular polyvinyl alcohol as a pore regulator and powdery phenol resin as a binder.
~he raw material for the ribbed layer may comprise a mixt~lre of 30 - 50% by weight of carbon fiber with an average fiber length of not more than 1 mm and diameter in the range of 3 - 30 llm, 20 - 50% by weight of granular polyvinyl alcohol, diameters of at leas-t 70% by weight of the particles being distributed in the range of 100 ~ 300 ~m, and 10 - 406 by weicJht of powdery phenol resin with diameter of not more than 100 ~m 3'~
thoroughly blended by a mixing mill such as a Henschel mixer.
~ The raw material for the non-ribbed layer of the ; inven-tion may comprise a similar mixture of the same components as above-rnentioned, except that the average fiber length of carbon fiber to be used is longer by 0.1 - 0.3 ~ and the mixed amount of the granular polyvinyl alcohol is larger by 5 - 20%
by weigh-t. Without this range of mixed amounts, a gas permeability and/or a mechanical strength of a substrate to be obtained will I be insufficient for a practical fuel cell.
The mixture for the ribbed layer is fed into a die having a proper configuration by a quantitative feeder such as a belt feeder in a predetermined amount so as to obtain a desired ; thickness. The mixture for the non-ribbed layer is then fed onto the supplied mixture of the ribbed layer by another feeder in an predetermined amount so as to make two layers.
The supplied mixtures are pressed by a heat press under the suitable conditions selected from die temperature of lO0 - 200C, molding pressure of 5 - lO0 kg/cm2 and molding period of 2 - 60 minutes. The suitable conditions for molding will be easily determined for those skilled in the art.
The pressed sheet is postcured without pressure for at least 2 hours and thereafter calcinated at 1500 - 2400C in an inert gas atmosphere. In the heating procedure, a slow increase of temperature between 300C and 700C is preferable since carbonization of polyvinyl alcohol and phenol resin is proceeded in the temperature region.
Th~ electrode suhstrate of the present invention is markedly suitable for a monopolar fuel cell and a fuel cell may be prepared from the substrates in a con~entional manner by stacking cells comprising two substrates and matrix layer there-between for holding phosphoric acid while disposing a separator plate~between two adjacent cells in contact with the ribbed surface of the substrate.
~ The electrode substrate of the invention has a low electric resistancet a low thermal resistance and a high mechanical strength due to a high bulk density of the ribbed layer, and the non-ribbed layer can hold suEficient amount o catalyst and elec-trolyt~ within pore~ therein due to a low bulk density, and -therefore a cleterioration of performance of an obtained fuel cell due to dissipation of phosphoric acid may be significantly reduced since the amount of phosphoric acid to be transferred by mutual difusion of phosphoric acid-hydrogen and phosphoric acid-oxygen or air is remarkably reduced~ Furthermore, a high limiting current density is obtained with the electrode substrate of the invention since the catalyst is effectively ~exerted because of large volume for holding catalyst.
The invention will be illustrated with respect to the following examples. It will be understood, however, that the invention must not be limited to these examples but various modiications may be carried out and those modifications will be also included within the scope of the present invention.
In the examples, the "porosity P t~)" was determined by the following equa-tion while assuming that the real density of a carbonaceous substrate was 1.6 g/cm3;
P = (l-ob/1.6) x 100 wherein Pb was the measured bulk density (g/cm3) of a specimen, the "bending strength (kg/cm2)" of a porous carbonaceous shaped article was determined according to Japanese Industrial St.andards (JIS) K-6911/1970 while using a specimen with a dimension of 100 x 10 x ~.5 mm, and the "pore diameter (l~m)" of a specimen was ~ measured by a mercury porosimeter (manufactured by Carlo Erba Strumentazione, Italia). The "gas permeability Qa (ml/cm2-hr-mm~q.)" was determined in the following manner: a cylindrical specimen of 90 mm in diameter was cut out from either layer of a subs-trate to be measured, the circumferential side surface of the specimen was treated with a thermosetting resin so that gas might not permeate therethrough, both longitudinal end surEaces of the specimen were then put between two cylindrical gas tubes with frange holding a gasket, a prede-termined amoun-t (10 l/min) of air was supplied from one end of the specimen to the o-ther end thereoE which was open to -the atmosphere, the pressure 1.oss between two ends o~ the specimen was measured by a manome-ter attached to the upstream of the gas tube and the gas permeability Qa was then calculated by the following equation;
1 19 ~
10 x 60 x 103 Qa 50.24 x ~p wherein ~p was the measured pressure loss (mmAq.) and 50.24 cm2 was a real area to be measured (a circle of 80 mm in diameter).
Yurther, the "bulk resistance PV (Qcm)" was determined in the following manner: both ends of a specimen were coated with an electroconductive coating material and an electrical resist-ance between two ends of the specimen was measured according to SRIS (Standards of Japan Rubber Association) 2301-1969, and then the bulk resistance was calculated by the following equation;
PV = R w~t/Q
wherein R was the measured resistance (Q) between the ends of the specimen, Q (cm) was a longitudinal leng~h (direction to be measured), and w (cm) and t (cm) were a horizontal and a vertical lengths, respectively, defining a cross section of the specimen.
_ g _ EXAMPLE 1:
A homogeneous mixture comprising 40 % by weiyh-t of short carbon fiber with an average fiber length of 0.45 mm and an average fiber diameter of 12 ~m (manufac-tured by Kureha Chemical Industry Co., Ltd.), 30% by weight of polyvinyl alcohol with an average particle diameter of 180 ~m (manufac-tured by The Nippon Synthetic Chemical Industry Co., Ltd.) as a pore regulator and 30% by weight of phenol resin (manufactured by Asahi Organic Material K.K.) as a binder was supplied into a die for press molding. Another homogeneous mix-ture comprising 45% by weight of the short carbon fiber, 35% by weight of the polyvinyl alcohol and 20% by weight of the phenol resin was fed onto the supplied mixture so as to be a double layer structure.
The mixture of double layer structure was pressed at 140C and 50 kg/cm2 for about 30 minutes and then calcinated at 2000C for about one hour.
The obtained electrode substrate had ribs with a thickness of 1 mm, a ribbed layer with a bulk density of 0.62 g/cm3, a porosity of 61%, an average pore diameter of 28 ~m and a thickness of 1.6 mm and a non-ribbed layer with a bulk density of 0.51 g/cm , a porosity of 68%, an average pore diameter of 33 ~Im and a thickness of 0.8 mm. The electrode substrate has the excellent physical properties such as a permeability of 320 ml/hr cm2-mmAq., a bending strenyth of 165 kg/cm2 and a bulk resistance of 24 x 10 Qcm.
-~3 EXAMPLE 2:
A mixture of 40% by weight of the short carbon fiber, 30% by weigh-t of the polyvinyl alcohol and 30% by weight of the phenol resin was Eed into a die and pressed at 140C and S0 kg/cm2 for about 30 minutes to form a ribbed layer.
Carbon fiber with an average length of 10 mm and an average fiber diameter of 12 ~m (manufactured by Kureha Chemical Industry Co., Ltd.) and polyvinyl alcohol fiber with an average fiber diameter of 10 ~m (manufactured by KURARAY CO., LTD.) were mixed in water and subjected to a paper machine followed by drying to obtain a carbon fiber paper.
The carbon fiber paper was laminated via phenol resin on the ribbed layer at 140C and 10 kg/cm2 for about 30 minutes.
The laminated sheet was calcinated at 2000C for about one hour.
The obtained electrode substrate had ribs with 1 mm in thickness, a ribbed layer with 0.62 g/cm3 in bulk density, 61% in porosity, 28 ~m in average pore diameter and 1.6 mm in thickness and a non-ribbed layer with 0.48 g/cm3 in bulk density, 70% in porosity, 42 ~m in average pore diameter and 0.4 mm in thickness. The physical properties were 360 ml/hr-cm2-mmAq. in gas permeability, 154 kg/cm2 in bending strength and 28 x 10 3 Q cm in bulk resistance.
EXAM~LE 3-A mixture of 40% by weight of the short carbon fiber, 30% by weight of the polyvinyl alcohol and 30% by weight of the phenol resin was supplied into a die and pressed at 140C and 50 kg/cm2 for about half an hour.
In the same die, a highly viscous mixture of S0%
by weight of liquid phenol resin (manufactured by Gunei Chemical K.K.), 30% by weight of carbon black with an average particle diameter of about 400A (manufac-tured by LION CORPOR~TION) and 20%
by weight of the polyvinyl alcohol was coated onto the pressed part and pressed at 140C and 10 kg/cm2 for about half an hour.
The pressed product was then calcinated at 2000C
for about one hour.
The obtained electrode substrate had ribs with l mm in thickness on the outer surface of a ribbed layer, a ribbed layer with a bulk density of 0.62 g/cm3, a porosity of 61%, an average pore diameter of 28 ~m and a thickness of 1.6 mm and a non-ribbed layer with a bulk density of 0.43 g/cm3, a porosity of 73%, an average pore diameter of 10 ~m and a thickness of O.4 mm. The electrode substrate had the physical properties such as a gas permeability of 420 ml/hr-cm2-mmAq., a bending strength of 142 kg/cm2 and a bulk resistance of 31 ~ 10 3 Qcm.
structure, that is herein termed by "a ribbed layer" and "a non-rib~ed layer", each layer having di~ferent properties from one another.
A ribbed electrode substrate for a monopolar Euel cell has been developed which has a ribbed surface on one side and on the other side a flat surface with a catalyst layer on the surface thereof. Such an electrode substrate is carbonaceous and porous as a whole. A cell is composed of two electrode substrates with a catalyst layer and a matrix therebetween for holding electrolyte. In a stack of such cells to form a fuel cell, a separator plate is disposed between two adjacent cells in contact with ribs of the substrate. Reactant gases (hydrogen as a fuel gas and oxygen or air) are fed via channels formed between the ribs and the separator plate and the gases diffuse from the ribbed surface to the flat surface in the electrode substra-te to reach the catalys-t layer.
For preparing such an electrode substra-te, the following I methods previously proposed may be used. For example, one method for preparing a general electrode substrate was proposed in Japanese Patent Application Laying Open No. 166354/82 wherein a mixture based on short carbonaceous fibers is pressed to form a porous shaped article. Another proposed method was described in Japanese Patent Publication No~ 18603~78 in which method a machined paper of carbon fibers is impregnated with an organic polymer solution and is made into a porous carbon fiber paper.
, i, A still another method for preparing an electrode substrate was proposed in United States Patent ~o. 3,829,327 wherein a web of carbon fibers is subjected to chernical vapor deposition of carbon to form a porous electrode substrate.
These electrode substrates have substantially homogeneous monolayer structures.
Such a homogeneous monolayer electrode substrate has however, disadvantages such as follows: with a high bulk density of a substrate, there is obtained a low limiting current density due to less diffusion of reactant gases and a rapid deterioration of performance of a fuel cell due to insufficient storage of electrolyte in the sub-strate, and therefore the life of a fuel cell is shortened;
on the other hand, disadvantages are high electric and thermal resistance and a low mechanical strength such as a bending strenqth, with a low bulk density of an electrode substrate.
It is an object of the present invention to provide an electrode substrate without such disadvantages.
According to the present invention, there is pro-vided a ribbed porous substrate for a fuel cell electrode, having a bending stength of not less than 50 kg/cm2 and a porosity of 50-80~, not less than 70~ of pores being open pores and not less than 60~ of the pores having a diameter in the range of 5-50 ~m, which comprises a double layer structure consisting essentially of a ribbed layer having ribs on one side thereof and a non-ribbed layer having flat surface on both side thereof and having a bulk density lower than the bulk density of the ribbed layer, the non-ribbed layer being laminated onto a flat s~rface of said ribbed layer and the laminated sheet being calcinated.
The ribbed layer of the electrode substrate of the S present invention has ribs on the outer surface thereof to be abutted to a separator plate in a fuel cell. The ribs may form together with the separator U-shaped channels for feeding reactant gases. The ribbed layer of the substrate preferably has a bulk density of 0.5 - 0.8 g/cm3 in order to provide the electrode substrate with a desired mechan-ical strength such as a bending strength of not less than 50 kg/cm2. The thickness of the ribbed layer except ribs is from 1/4 to 5/6 of the total thickness of the electrode substrate minus a thickness of the ribs.
The non-ribbed layer of the electrode substrate according to the invention has a flat surface on the outer side thereof and a bulk density lower than the bulk density of the ribbed layer. The bulk density of the non-ribbed layer is preferably in the range of 0.4 - 0.6 g/cm3 for a desired diffusion or permeation of reactant gases and for a desired holding of a given amount of catalyst and electrolyte.
Generally, it is desirable for a fuel cell that a good diffusion of reactant gases through pores in the electrode substrate is maintained in the whole part of the substrate. In the present invention, the electrode sub-strate is porous as a whole and has a porosity of 50 - 80 and not less than 70~ of L?~ t ~i the pores are open pores. Furthermore, the diameter of pores in the substrate of the invention is distributed in a narrow range, that is to say, not less than 60% of the pores have diameter in the range of 5 - 50 ~m, this sharp distribution of pore diameter resulting in a better application of the e]ectrode substrate of the invention to a fuel cell.
The electrode substrate of the present invention may be prepared by various methods, for example pressing process, paper-machining process or coating process. In the pressing process, raw materials for each layer, i.e. a non-ribbed layer and a ribbed layer, are separately supplied in-to a die having a predetermined configuration and pressed while heating. In the paper-machining process, a machined paper of mixed carbon fibers as a non-ribbed layer is laminated onto a pressed part prepared from the same raw material as the pressing process for a ribbed layer. In the third method (the coating process), a mixture of a filler e.g. active carbon or carbon black and a thermosetting resin e.g. a liquid phenol resin (in an alcohol as a solvent~
as a non-ribbed layer is coated onto a pressed part prepared from the same raw material as the pressing process for a ribbed layer.
A raw material for the ribbed layer of the invention may be appropriately selected from carbon fiber and active carbon for a filler, a polymer substance with a sharp distribution of particle diameters such as polyvinyl alcohol, polyethylene, polypropylene, polyvinyl chloride and sugar for a pore regulator and thermosetting resins such as phenol resin for a binder.
A raw material for the non-ribbed layer of the invention may be suitably selected Erom known materials to be appropriately used depending on to the processes. In the pressing process, a filler may be carbon fiber, granular active carbon or the like, a pore regulator may be the same as for the ribbed layer and a binder may be phenol resin or the like. In the paper-machining process, a filler may be carbon fiber or the like, ~ a pore regulator may be polyvinyl alcohol fiber or the like and a binder may be liquid phenol resin or the like. In the coating process, a filler may be granular active carbon, carbon black or the like, a pore regulator may be the same as -the pressing process and a binder may be the same as the paper-machining process.
As an example of the preparation process of the electrode substrate of the present invention will be described hereinafter in more detail, particularly the pressing process using short carbon fiber as a filler, granular polyvinyl alcohol as a pore regulator and powdery phenol resin as a binder.
~he raw material for the ribbed layer may comprise a mixt~lre of 30 - 50% by weight of carbon fiber with an average fiber length of not more than 1 mm and diameter in the range of 3 - 30 llm, 20 - 50% by weight of granular polyvinyl alcohol, diameters of at leas-t 70% by weight of the particles being distributed in the range of 100 ~ 300 ~m, and 10 - 406 by weicJht of powdery phenol resin with diameter of not more than 100 ~m 3'~
thoroughly blended by a mixing mill such as a Henschel mixer.
~ The raw material for the non-ribbed layer of the ; inven-tion may comprise a similar mixture of the same components as above-rnentioned, except that the average fiber length of carbon fiber to be used is longer by 0.1 - 0.3 ~ and the mixed amount of the granular polyvinyl alcohol is larger by 5 - 20%
by weigh-t. Without this range of mixed amounts, a gas permeability and/or a mechanical strength of a substrate to be obtained will I be insufficient for a practical fuel cell.
The mixture for the ribbed layer is fed into a die having a proper configuration by a quantitative feeder such as a belt feeder in a predetermined amount so as to obtain a desired ; thickness. The mixture for the non-ribbed layer is then fed onto the supplied mixture of the ribbed layer by another feeder in an predetermined amount so as to make two layers.
The supplied mixtures are pressed by a heat press under the suitable conditions selected from die temperature of lO0 - 200C, molding pressure of 5 - lO0 kg/cm2 and molding period of 2 - 60 minutes. The suitable conditions for molding will be easily determined for those skilled in the art.
The pressed sheet is postcured without pressure for at least 2 hours and thereafter calcinated at 1500 - 2400C in an inert gas atmosphere. In the heating procedure, a slow increase of temperature between 300C and 700C is preferable since carbonization of polyvinyl alcohol and phenol resin is proceeded in the temperature region.
Th~ electrode suhstrate of the present invention is markedly suitable for a monopolar fuel cell and a fuel cell may be prepared from the substrates in a con~entional manner by stacking cells comprising two substrates and matrix layer there-between for holding phosphoric acid while disposing a separator plate~between two adjacent cells in contact with the ribbed surface of the substrate.
~ The electrode substrate of the invention has a low electric resistancet a low thermal resistance and a high mechanical strength due to a high bulk density of the ribbed layer, and the non-ribbed layer can hold suEficient amount o catalyst and elec-trolyt~ within pore~ therein due to a low bulk density, and -therefore a cleterioration of performance of an obtained fuel cell due to dissipation of phosphoric acid may be significantly reduced since the amount of phosphoric acid to be transferred by mutual difusion of phosphoric acid-hydrogen and phosphoric acid-oxygen or air is remarkably reduced~ Furthermore, a high limiting current density is obtained with the electrode substrate of the invention since the catalyst is effectively ~exerted because of large volume for holding catalyst.
The invention will be illustrated with respect to the following examples. It will be understood, however, that the invention must not be limited to these examples but various modiications may be carried out and those modifications will be also included within the scope of the present invention.
In the examples, the "porosity P t~)" was determined by the following equa-tion while assuming that the real density of a carbonaceous substrate was 1.6 g/cm3;
P = (l-ob/1.6) x 100 wherein Pb was the measured bulk density (g/cm3) of a specimen, the "bending strength (kg/cm2)" of a porous carbonaceous shaped article was determined according to Japanese Industrial St.andards (JIS) K-6911/1970 while using a specimen with a dimension of 100 x 10 x ~.5 mm, and the "pore diameter (l~m)" of a specimen was ~ measured by a mercury porosimeter (manufactured by Carlo Erba Strumentazione, Italia). The "gas permeability Qa (ml/cm2-hr-mm~q.)" was determined in the following manner: a cylindrical specimen of 90 mm in diameter was cut out from either layer of a subs-trate to be measured, the circumferential side surface of the specimen was treated with a thermosetting resin so that gas might not permeate therethrough, both longitudinal end surEaces of the specimen were then put between two cylindrical gas tubes with frange holding a gasket, a prede-termined amoun-t (10 l/min) of air was supplied from one end of the specimen to the o-ther end thereoE which was open to -the atmosphere, the pressure 1.oss between two ends o~ the specimen was measured by a manome-ter attached to the upstream of the gas tube and the gas permeability Qa was then calculated by the following equation;
1 19 ~
10 x 60 x 103 Qa 50.24 x ~p wherein ~p was the measured pressure loss (mmAq.) and 50.24 cm2 was a real area to be measured (a circle of 80 mm in diameter).
Yurther, the "bulk resistance PV (Qcm)" was determined in the following manner: both ends of a specimen were coated with an electroconductive coating material and an electrical resist-ance between two ends of the specimen was measured according to SRIS (Standards of Japan Rubber Association) 2301-1969, and then the bulk resistance was calculated by the following equation;
PV = R w~t/Q
wherein R was the measured resistance (Q) between the ends of the specimen, Q (cm) was a longitudinal leng~h (direction to be measured), and w (cm) and t (cm) were a horizontal and a vertical lengths, respectively, defining a cross section of the specimen.
_ g _ EXAMPLE 1:
A homogeneous mixture comprising 40 % by weiyh-t of short carbon fiber with an average fiber length of 0.45 mm and an average fiber diameter of 12 ~m (manufac-tured by Kureha Chemical Industry Co., Ltd.), 30% by weight of polyvinyl alcohol with an average particle diameter of 180 ~m (manufac-tured by The Nippon Synthetic Chemical Industry Co., Ltd.) as a pore regulator and 30% by weight of phenol resin (manufactured by Asahi Organic Material K.K.) as a binder was supplied into a die for press molding. Another homogeneous mix-ture comprising 45% by weight of the short carbon fiber, 35% by weight of the polyvinyl alcohol and 20% by weight of the phenol resin was fed onto the supplied mixture so as to be a double layer structure.
The mixture of double layer structure was pressed at 140C and 50 kg/cm2 for about 30 minutes and then calcinated at 2000C for about one hour.
The obtained electrode substrate had ribs with a thickness of 1 mm, a ribbed layer with a bulk density of 0.62 g/cm3, a porosity of 61%, an average pore diameter of 28 ~m and a thickness of 1.6 mm and a non-ribbed layer with a bulk density of 0.51 g/cm , a porosity of 68%, an average pore diameter of 33 ~Im and a thickness of 0.8 mm. The electrode substrate has the excellent physical properties such as a permeability of 320 ml/hr cm2-mmAq., a bending strenyth of 165 kg/cm2 and a bulk resistance of 24 x 10 Qcm.
-~3 EXAMPLE 2:
A mixture of 40% by weight of the short carbon fiber, 30% by weigh-t of the polyvinyl alcohol and 30% by weight of the phenol resin was Eed into a die and pressed at 140C and S0 kg/cm2 for about 30 minutes to form a ribbed layer.
Carbon fiber with an average length of 10 mm and an average fiber diameter of 12 ~m (manufactured by Kureha Chemical Industry Co., Ltd.) and polyvinyl alcohol fiber with an average fiber diameter of 10 ~m (manufactured by KURARAY CO., LTD.) were mixed in water and subjected to a paper machine followed by drying to obtain a carbon fiber paper.
The carbon fiber paper was laminated via phenol resin on the ribbed layer at 140C and 10 kg/cm2 for about 30 minutes.
The laminated sheet was calcinated at 2000C for about one hour.
The obtained electrode substrate had ribs with 1 mm in thickness, a ribbed layer with 0.62 g/cm3 in bulk density, 61% in porosity, 28 ~m in average pore diameter and 1.6 mm in thickness and a non-ribbed layer with 0.48 g/cm3 in bulk density, 70% in porosity, 42 ~m in average pore diameter and 0.4 mm in thickness. The physical properties were 360 ml/hr-cm2-mmAq. in gas permeability, 154 kg/cm2 in bending strength and 28 x 10 3 Q cm in bulk resistance.
EXAM~LE 3-A mixture of 40% by weight of the short carbon fiber, 30% by weight of the polyvinyl alcohol and 30% by weight of the phenol resin was supplied into a die and pressed at 140C and 50 kg/cm2 for about half an hour.
In the same die, a highly viscous mixture of S0%
by weight of liquid phenol resin (manufactured by Gunei Chemical K.K.), 30% by weight of carbon black with an average particle diameter of about 400A (manufac-tured by LION CORPOR~TION) and 20%
by weight of the polyvinyl alcohol was coated onto the pressed part and pressed at 140C and 10 kg/cm2 for about half an hour.
The pressed product was then calcinated at 2000C
for about one hour.
The obtained electrode substrate had ribs with l mm in thickness on the outer surface of a ribbed layer, a ribbed layer with a bulk density of 0.62 g/cm3, a porosity of 61%, an average pore diameter of 28 ~m and a thickness of 1.6 mm and a non-ribbed layer with a bulk density of 0.43 g/cm3, a porosity of 73%, an average pore diameter of 10 ~m and a thickness of O.4 mm. The electrode substrate had the physical properties such as a gas permeability of 420 ml/hr-cm2-mmAq., a bending strength of 142 kg/cm2 and a bulk resistance of 31 ~ 10 3 Qcm.
Claims (3)
1. A ribbed porous substrate for a fuel cell electrode, having a bending stength of not less than 50 kg/cm2 and a porosity of 50-80%, not less than 70% of pores being open pores and not less than 60% of the pores having a diameter in the range of 5-50 µm, which comprises a double layer structure consisting essentially of a ribbed layer having ribs on one side thereof and a non-ribbed layer having flat surface on both side thereof and having a bulk density lower than the bulk density of the ribbed layer, the non-ribbed layer being laminated onto a flat surface of said ribbed layer and the laminated sheet being calcinated .
2. The substrate of claim 1, in which the bulk density of the ribbed layer is 0.5-0.8 g/cm3 and the bulk density of the non-ribbed layer is 0.4-0.6 g/cm3.
3. The substrate of claim 1 or 2, in which thickness of the ribbed layer excluding the height of the ribs ranges from 1/4 - 5/6 of the total substrate thickness when the height of the ribs is not included in said total substrate thickness.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP146691/1982 | 1982-08-24 | ||
| JP57146691A JPS5937662A (en) | 1982-08-24 | 1982-08-24 | Electrode substrate for monopolar type fuel cell with two-layer structure |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1194926A true CA1194926A (en) | 1985-10-08 |
Family
ID=15413385
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000435102A Expired CA1194926A (en) | 1982-08-24 | 1983-08-22 | Ribbed substrate for fuel cell electrode |
Country Status (6)
| Country | Link |
|---|---|
| US (1) | US4547418A (en) |
| JP (1) | JPS5937662A (en) |
| CA (1) | CA1194926A (en) |
| DE (1) | DE3330378A1 (en) |
| FR (1) | FR2532477B1 (en) |
| GB (1) | GB2126410B (en) |
Families Citing this family (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5946763A (en) * | 1982-09-10 | 1984-03-16 | Kureha Chem Ind Co Ltd | Two-layered electrode base plate for monopolar fuel cell |
| JPS6123780A (en) * | 1984-07-12 | 1986-02-01 | Kureha Chem Ind Co Ltd | Oxygen cathode for electrolyzing alkali chloride and its manufacture |
| US4794043A (en) * | 1985-04-30 | 1988-12-27 | Kureha Kagaku Kogyo Kabushiki Kaisha | Carbon product comprising carbonaceous materials joined together, said carbon product for electrode substrate of fuel cells and process for production thereof |
| US4818640A (en) * | 1985-09-25 | 1989-04-04 | Kureha Kagaku Kogyo Kabushiki Kaisha | Carbonaceous composite product produced by joining carbonaceous materials together by tetrafluoroethylene resin, and process for producing the same |
| US4913706A (en) * | 1988-09-19 | 1990-04-03 | International Fuel Cells Corporation | Method for making a seal structure for an electrochemical cell assembly |
| DK166747B1 (en) * | 1989-12-05 | 1993-07-05 | Topsoe Haldor As | FUEL CELL AND FUEL CELL STABLE |
| DE19940351B4 (en) * | 1998-08-26 | 2004-01-08 | Aisin Seiki K.K., Kariya | Method of making a carbon sheet and an electrode |
| US20020192539A1 (en) * | 2000-10-31 | 2002-12-19 | Sususmu Kobayashi | High polymer electrolyte fuel cell |
| US6890679B2 (en) * | 2002-08-23 | 2005-05-10 | Fuelcell Energy, Inc. | Dual-porosity ribbed fuel cell cathode |
| KR101351392B1 (en) * | 2011-07-13 | 2014-01-16 | 삼성에스디아이 주식회사 | Electrode for fuel cell, and membrane-electrode assembly and fuel cell system including the same |
| WO2013095380A1 (en) * | 2011-12-20 | 2013-06-27 | United Technologies Corporation | Flow battery with carbon paper |
Family Cites Families (21)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL247471A (en) * | 1959-01-22 | 1900-01-01 | ||
| US3423247A (en) * | 1963-06-07 | 1969-01-21 | Union Carbide Corp | Porous conductive electrode having at least two zones |
| US3385780A (en) * | 1964-07-10 | 1968-05-28 | Exxon Research Engineering Co | Porous dual structure electrode |
| GB1182479A (en) * | 1966-11-30 | 1970-02-25 | Matsushita Electric Ind Co Ltd | Improvements in or relating to Gas Diffusion Electrodes for Fuel Cells or Batteries |
| US3556856A (en) * | 1968-08-22 | 1971-01-19 | Union Carbide Corp | Three-layer fuel cell electrode |
| CH510332A (en) * | 1969-11-12 | 1971-07-15 | Bbc Brown Boveri & Cie | Fuel cell |
| US3829327A (en) * | 1972-07-03 | 1974-08-13 | Kreha Corp | Carbon paper |
| JPS5318603B2 (en) * | 1973-07-10 | 1978-06-16 | ||
| US3956014A (en) * | 1974-12-18 | 1976-05-11 | United Technologies Corporation | Precisely-structured electrochemical cell electrode and method of making same |
| JPS5267737A (en) * | 1975-12-04 | 1977-06-04 | Oval Eng Co Ltd | Electrode |
| US4115627A (en) * | 1977-08-15 | 1978-09-19 | United Technologies Corporation | Electrochemical cell comprising a ribbed electrode substrate |
| IT1111479B (en) * | 1978-06-20 | 1986-01-13 | Fiat Spa | GRAPHITE Porous COMPOSITE STRUCTURE ELECTRODE RESIN FOR APPLICATION IN ELECTROCHEMICAL SYSTEMS |
| US4267137A (en) * | 1978-12-11 | 1981-05-12 | United Technologies Corporation | Method for molding sheet material with parallel ribs on one side |
| DE2928911A1 (en) * | 1979-06-29 | 1981-01-29 | Bbc Brown Boveri & Cie | ELECTRODE FOR WATER ELECTROLYSIS |
| US4279970A (en) * | 1980-02-20 | 1981-07-21 | Electric Power Research Institute, Inc. | Electrochemical cell including ribbed electrode substrates |
| JPS57166354A (en) * | 1981-04-01 | 1982-10-13 | Kureha Chemical Ind Co Ltd | Porous carbon formed body and manufacture |
| US4374906A (en) * | 1981-09-29 | 1983-02-22 | United Technologies Corporation | Ribbed electrode substrates |
| US4426340A (en) * | 1981-09-29 | 1984-01-17 | United Technologies Corporation | Process for fabricating ribbed electrode substrates and other articles |
| JPS58100364A (en) * | 1981-12-10 | 1983-06-15 | Hitachi Ltd | Porous electrode plate for fuel cell |
| JPS58117649A (en) * | 1981-12-29 | 1983-07-13 | Kureha Chem Ind Co Ltd | Manufacture of electrode substrate of fuel cell |
| JPS5927466A (en) * | 1982-08-06 | 1984-02-13 | Tokyo Electric Power Co Inc:The | Fuel cell |
-
1982
- 1982-08-24 JP JP57146691A patent/JPS5937662A/en active Granted
-
1983
- 1983-08-15 US US06/523,661 patent/US4547418A/en not_active Expired - Lifetime
- 1983-08-22 CA CA000435102A patent/CA1194926A/en not_active Expired
- 1983-08-22 GB GB08322541A patent/GB2126410B/en not_active Expired
- 1983-08-23 FR FR8313592A patent/FR2532477B1/en not_active Expired
- 1983-08-23 DE DE19833330378 patent/DE3330378A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| GB8322541D0 (en) | 1983-09-21 |
| JPS5937662A (en) | 1984-03-01 |
| US4547418A (en) | 1985-10-15 |
| GB2126410B (en) | 1985-12-18 |
| JPH0449746B2 (en) | 1992-08-12 |
| DE3330378C2 (en) | 1987-05-27 |
| DE3330378A1 (en) | 1984-03-01 |
| GB2126410A (en) | 1984-03-21 |
| FR2532477B1 (en) | 1987-04-10 |
| FR2532477A1 (en) | 1984-03-02 |
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